This disclosure relates to a cooling arrangement for a high power electric machine, such as a generator used in aerospace applications.
One type of generator liquid cooling arrangement provides annular cooling channels on an inner diameter of a housing adjacent to an outer diameter of a stator. Multiple annular cooling channels are axially spaced relative to one another along the housing about the stator. Cooling oil is supplied to the cooling channels through an inlet in the housing. The flow path through the annular cooling channels is tortuous such that the flow direction reverses in each axially successive annular cooling channel.
The stator typically includes a sleeve supported on the stator windings and in contact with the housing, which operates to seal the annular cooling channels relative to one another. At elevated operating temperatures, the housing experiences more thermal growth than the sleeve, which creates a radial gap between the annular cooling channels and the sleeve. Cooling fluid is permitted to leak between the annular cooling channels, causing the cooling fluid in adjacent annular cooling channels to flow in the same direction.
The stator typically includes end turns that extend opposite one another from a main stack. A rotating liquid spray is often used to cool stator end turns. Cooling fluid cast from the rotor inner diameter by centrifugal force coats the end turns. The cooling fluid falls from the end turns back onto the rotor.